Fwd: API REVIEW: Weak event handler

[Sven Reimers]

Ups, forgot the mailinglist reply...

Sorry for that.

Sven


---------- Forwarded message ----------
From: Sven Reimers <sven.reimers at gmail.com>
Date: Tue, Jun 12, 2012 at 4:55 PM
Subject: Re: API REVIEW: Weak event handler
To: Lubomir Nerad <lubomir.nerad at oracle.com>


Any reason why

public static <T extends Event> WeakEventHandler<T>
create(EventHandler<T> eventHandler) { ... }

is not

public static <T extends Event> EventHandler<T> create(EventHandler<T>
eventHandler) { ... }

Is there a special use case why the usaer of the API should know about
the implementation? From my  point of view just hide it behind a
static method call on EventHandler itself..

Regards

Sven

On Tue, Jun 12, 2012 at 1:47 PM, Lubomir Nerad <lubomir.nerad at oracle.com> wrote:
> Hi All,
>
> there is a request to add a WeakEventHandler to the API
> (http://javafx-jira.kenai.com/browse/RT-13706). This will be a simple
> wrapper for the target event handler to which it will delegate the handle
> calls. It will reference the target weakly and so it won't prevent it from
> being garbage collected.
>
> My proposal for this class is:
>
> package javafx.event;
>
> public final class WeakEventHandler<T extends Event>
>        extends WeakReference<EventHandler<T>>
>        implements EventHandler<T> {
>
>    private WeakEventHandler(EventHandler<T> eventHandler) { ... }
>
>    @Override public void handle(final T event) { ... }
>
>    public static <T extends Event> WeakEventHandler<T>
> create(EventHandler<T> eventHandler) { ... }
> }
>
> I decided to make this class both an EventHandler (implements) and a
> WeakReference (extends). Mainly I needed to have some way how to test from
> event handler containers whether the target event handler for a stored
> wrapper has been garbage collected and so the wrapper can be removed as
> well. Extending WeakReference adds the required method (WeakReference.get())
> and saves some object instances. It also brings the clear method, which can
> simplify testing of this feature.
>
> WeakEventHandler instances will be created through the create factory
> method. This is to avoid repetition of the event type during event handler
> registration.
>
> So instead of:
> node.setOnMousePressed(new WeakEventHandler<MouseEvent>(new
> EventHandler<MouseEvent>() { ... }));
>
> we can use:
> node.setOnMousePressed(WeakEventHandler.create(new
> EventHandler<MouseEvent>() { ... }));
>
> I also considered to define the WeakEventHandler as an interface which
> extends EventHandler, but adds no additional methods. Then leave it to event
> handler containers to reference such event handlers weakly. This has very
> simple and direct usage, but also its own problems. We can discuss it
> further if you find this solution preferred to the wrapper approach.
>
> Thanks,
> Lubo
>



--
Sven Reimers

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-- 
Sven Reimers

* Senior Expert Software Architect
* NetBeans Dream Team Member: http://dreamteam.netbeans.org
* NetBeans Governance Board Member: http://netbeans.org/about/os/governance.html
* Community Leader  NetBeans: http://community.java.net/netbeans
                              Desktop Java:
http://community.java.net/javadesktop
* Duke's Choice Award Winner 2009
* Blog: http://nbguru.blogspot.com

* XING: https://www.xing.com/profile/Sven_Reimers8
* LinkedIn: http://www.linkedin.com/in/svenreimers

Join the NetBeans Groups:
* XING: http://www.xing.com/group-20148.82db20
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* LinkedIn: http://www.linkedin.com/groups?gid=1860468
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